Version 1.0, new agent recipe, many fixes/tests

- Bump logstash to version 1.4.2.
- Added top-level `agent` recipe and test suite, intended for running logstash-agent on a regular server. Uses `elasticsearch::search_discovery` to find and list elk cluster nodes (can override this as well, see elasticsearch cookbook for how). Agent uses lumberjack protocol by default and requires a keypair before converging.
- Switch nodes to communicate using node protocol on `eslocal:9300` between logstash and elasticsearch on the same box.
- Write chefspec tests for default (server nodes) and agent to 100% coverage. Add `chef-sugar` to `Gemfile` to be able to converge with chefspec and fauxhai.
- Drop dependency on `logstash_stack` (didn't need to be there any longer, wasn't used).
- Nodes no longer forward directly to logstash on the remote side, they forward to a local logstash listening for syslog.
- Bugfix: `/etc/hosts` is now correctly populated for all classes of elkstack, not just multi-node.
- Bugfix: The `newrelic` plugin now monitors against eslocal, not localhost.